I have a problem understanding nested classes in tc (traffic control).
To introduce the problem, I briefly describe how I think the tc works.
There are qdiscs, classes and filters. A qdisc can have classes,
and filters configured for this qdisc classify packets. When a packet
is enqueue to a qdisc, filters decide which class the packet belongs
to, i.e. filters classify packets. Each class has a qdisc, by default
the pfifo class, and so classifying implies enqueing a packet in the
queue of class the packet was classified to.
Therefore I would claim that a class cannot have another class as a
child, because the child should be a qdisc. However, Example 1 shows
that I'm wrong.
Example 1
---------
tc qdisc add dev eth0 root handle 1:0 htb
tc class add dev eth0 parent 1:0 classid 1:1 htb rate 10mbit
tc class add dev eth0 parent 1:1 classid 1:2 htb rate 1mbit
In this example class 1:1 is a parent of both classes 1:2 and 1:3.
QUESTION 1: Does class 1:1 have a queue?
Example 2 implements the same functionality as Example 1, I think.
Example 2
---------
tc qdisc add dev eth0 root handle 1:0 htb
tc class add dev eth0 parent 1:0 classid 1:1 htb rate 10mbit
tc qdisc add dev eth0 parent 1:1 handle 2:0 htb
tc class add dev eth0 parent 2:0 classid 2:1 htb rate 1mbit
QUESTION 2: Is there a difference between Example 1 and Example 2?
QUESTION 3: What is "-d" for in "tc -s -d qdisc"
QUESTION 4: How can I view the statistics for default queues of
classes, those pfifo queues? "tc -s qdisc" doesn't show them.
QUESTION 5: Why in filters there is used "flowid" instead of "parent"?
I would appreciate it if someone could answer my questions.
--
Ireneusz (Irek) Szczesniak
http://www.irkos.org
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